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Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Naturally Occurring Toxins 3

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This is the seventeenth post based upon educational sessions and syllabus material presented at the Wilderness Medical Society Annual Meeting & 25th Anniversary held in Snowmass, Colorado from July 25 to 30, 2008. It includes information from a lecture entitled “Beautiful But Deadly: Naturally Occurring Toxins,” delivered by Edward J. (“Mel”) Otten, MD, FACMT, FAWM, who is Professor Of Emergency Medicine and Pediatrics, as well as Director of the Division of Toxicology in the medical center at the University of Cincinnati. Mel is also a past President of the Wilderness Medical Society.

VENOMOUS ANIMALS

Arthropods comprise the largest group of animals and contains 60% of all living species. Many arthropods are venomous. They may bite, sting or secrete venom through pores or hairs. Caterpillars, ticks, mites, water bugs, ants, bees, spiders, scorpions, centipedes, kissing bugs, millipedes and many others are included in this group.

Hymenoptera

The class Hymenoptera contains the most commonly encountered venomous animals and accounts for most of the morbidity and mortality. These are the bees, wasps, hornets, and ants. The amount of venom that is deposited is usually small and the serious clinical effects are related to manifestations of an allergic reaction.

The venom apparatus is a modified ovipositor and the venom, with the
exception of that of fire ants, is mainly protein in nature but also contains
various peptides, amines and other low molecular weight substances. Fire ant (Solenopsis invicta) venom is 99% alkaloid, which is unusual in the animal kingdom. The venom of Hymenoptera is deposited in the victim via the sting and may produce an immunoglobulin E (IgE) mediated antigen-antibody reaction and an acute anaphylactic (severe allergic) response in the victim. This is the usual cause of death and is not related to the toxicity of the venom, but rather to the immune response mounted by the victim.

Honey bee venom causes an increase in the amount of histamine released. There is only a small degree of cross reactivity with the venom of wasps and hornets. The honey bee has large barbs on her sting, which result in the entire venom apparatus being removed during the stinging process and the bee dying. This causes a release from the bee of a pheromone that attracts more bees. More stings may occur. The sting is usually painful and may become red and swollen. Some victims may have a diffuse reaction involving an entire limb that resembles cellulitis.

Antihistamines may be used to treat the symptoms. Victims who have an anaphylactic response may have airway spasm, a raised red rash (hives), very low blood pressure, coma and cardiac arrest. The treatment is epinephrine injection, oxygen and airway control, and fluid administration, and must be instituted as soon as possible after the sting(s) to be effective.

The Rule of Hymenoptera: It's not the toxin - it's the allergic reaction that is dangerous.

Arachnids

There are more than 20,000 species of spider in the world, and all of them are venomous. Fortunately for humans, only a few of these spiders have the ability to penetrate human skin. There are about 800 species of scorpion, and only a few of these cause serious envenomation in humans.

The two most dangerous spiders in the United States are the black widow (Latrodectus mactans) and the brown recluse (Loxosceles reclusa). Black widow venom causes patients to present with severe muscle spasms, high blood pressure, excessive salivation, seizures and coma. A horse serum-derived antivenom is available and should be used if benzodiazepines (e.g., diazepam [Valium]) and/or calcium gluconate are not effective.

Venom from Loxosceles species contains a number of proteins, including sphingomyelinase D, a rare enzyme even in venomous animals. There are no specific neurotoxins and most of the clinical signs are necrotic skin lesions or allergic reactions. There is no specific foolproof treatment, but oral dapsone has been advocated by some clinicians to limit the amount of tissue destruction.

The only dangerous scorpion in the United States is the Arizona bark scorpion Centruroides exilicauda. This is a small scorpion with a potent venom that enhances repetitive firing of axons by sodium channel
activation.

The Rule of Scorpions: The large the scorpion, the more local reaction; the smaller the scorpion the more dangerous from a generalized illness perspective.

Reptiles

Venomous snakes have always struck fear in the hearts of humans. Perhaps this is because man may have evolved on the plains of Africa, where reside some of the most dangerous snakes. There are about 3000 species of snakes, but only about 300 are venomous, and these are found in five families. Only two of these families are represented in the United States. These are the pit vipers (Crotalidae) and the coral snakes (Elapidae).

Pit vipers can be identified by a small heat sensitive pit found between the eye and the nostril. They cannot be identified by their shape or color pattern. This family includes the rattlesnakes, copperheads, water moccasins, and pygmy rattlesnakes. The Eastern coral snake can be identified by the pattern of the colored bands on its body. If a red band is next to a yellow band, the snake is venomous. The only venomous lizards in the world are found in the American Southwest in the form of Gila monsters or beaded lizards.

Reptile venoms are extremely complex and may contain several classes of compounds that act in a number of ways. For example, pit viper venom contains a number of enzymes that cause local tissue destruction and deranged blood clotting (e.g., excessive bleeding) as well as small polypeptides that are cardiotoxic and neurotoxic. The clinical presentation may vary depending on the species, and a number of victims suffer multi-system involvement.

Not all persons envenomed by pit vipers need to be given antivenom. Only snakebite victims with moderate to severe reactions should be treated with the horse serum-derived antivenin. The antivenin must be given intravenously, and the clinical response determines the dose. Prior to treatment, most intended recipients are skin tested for horse serum allergy, but a significant number of persons who test “negative” may still suffer an allergic reaction to antivenom. Therefore, it is mandatory that everyone receiving antivenom be monitored closely for anaphylaxis. Most patients receiving more that 7 vials of traditional antivenom develop a reaction known as serum sickness.

Coral snake venom is primarily neurotoxic. Most victims of coral snakebite will need to receive antivenin. A recent problem in the United States is the importation of extremely dangerous venomous snakes (cobras, kraits, mambas, adders) from foreign countries. These snakes are difficult for U.S. medical personnel to identify, and appropriate antivenom is not readily available. Local zoo professionals or herpetologists at universities may be helpful in identifying these snakes. The Antivenin Index from the Arizona Poison Control Center may be helpful in locating and obtaining antivenom.

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.

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